It has emerged that Prime Minister David Cameron’s insistence that an Australian-style points-based immigration system would be bad for Britain directly contradicts a pledge to introduce such a system in the Conservative Party’s 2005 manifesto – which Mr. Cameron wrote.

The Leave campaign calling on Britons to vote to exit the European Union (EU) gained momentum this week as it went in hard on immigration, which it argues cannot be brought under control unless Britain leaves the EU.

Two of the campaign’s leading figures, Justice Secretary Michael Gove and former London Mayor Boris Johnson, pledged to introduce an Australian-style points-based system if Britain is freed from Brussels’s open borders commitments, ensuring that migrants to the country are awarded visas on merit, not nationality.

But the Prime Minister, who is leading the campaign to keep Britain within the EU, trashed the policy calling it the “wrong approach” and claiming it would “crash the economy”.

“This will give priority to people with the skills Britain needs,” the manifesto stated.

The man behind the manifesto: David Cameron MP.

“Our out-of-control immigration system encourages people smugglers and penalises genuine refugees,” the manifesto laments, and it decries the then rate of immigration – 150,000 net arriving in the UK each year – as proof that the then Labour “government has lost effective control of our borders”. Under Mr. Cameron, migration levels have been running at twice that figure.

The solution, it claimed, was to “take proper control of our borders,” which would include introducing the Australian-style system.

Conservative historian Lord Lexden, who pointed out the prime minister’s change of heart in a letter to the Telegraph today, asked simply: “Why is that policy now wrong?”

This week Mr. Gove and Mr. Johnson made the very same point, pledging: “By the next general election, we will create a genuine Australian-style points-based immigration system.

“The automatic right of all EU citizens to come to live and work in the UK will end, as will EU control over vital aspects of our social security system. EU citizens will be subject to legislation made by those we elect in Westminster, not in Brussels. We could then create fairness between EU citizens and others, including those from Commonwealth countries.”

Mr. Cameron slammed the policy, telling BBC Radio 5 live: “Australia has more migration per head than we do here in the UK, so I think it’s the wrong approach.”

And he argued that it would disadvantage British citizens, saying: “I also think if we were to say to Europeans they needed work permits to come to Britain, European countries would say to us we need work permits to go and work there.

“So not only would we crash our economy, we’d also reduce opportunities to work in other countries.”

The volte-face on the Australian system is not the only u-turn Mr. Cameron has made over the last decade.

The 2005 manifesto states that the rate of migration must be democratically set and controlled, stating: “There should be popular consent for further demographic change. And the best way to secure continuing support for future migration is by showing that government has control of our borders. Refusing to set a limit on new migrants is irresponsible politics.”

But pressed by Faisal Islam on Sky News last night on when annual immigration figures would be brought within the government’s official target of under 100,000, Mr. Cameron floundered.

He insisted that the target could be reached while remaining within the EU – if the rate of British people leaving the country increased sufficiently. “There have been years, and there will be again, when people from Britain choose to go and work overseas,” he said.

But when pressed on when that might happen, could only reply: “I’m not going to put a date on it”.

A little-known backbench MP when the manifesto was written, Mr. Cameron would go on, just months after the Conservatives lost that election under the leadership of Michael Howard, to take the reins of his party.

Somewhat ironically in the light of recent events, at the time, the Liberal Democrat’s then-party president Simon Hughes said that the manifesto marked him out as a “convinced anti-European”.